mirror of
https://github.com/Divested-Mobile/DivestOS-Build.git
synced 2024-12-20 21:34:24 -05:00
76 lines
2.9 KiB
Plaintext
76 lines
2.9 KiB
Plaintext
From 95e91b831f87ac8e1f8ed50c14d709089b4e01b8 Mon Sep 17 00:00:00 2001
|
|
From: Davidlohr Bueso <dave@stgolabs.net>
|
|
Date: Mon, 27 Feb 2017 14:28:24 -0800
|
|
Subject: ipc/shm: Fix shmat mmap nil-page protection
|
|
|
|
The issue is described here, with a nice testcase:
|
|
|
|
https://bugzilla.kernel.org/show_bug.cgi?id=192931
|
|
|
|
The problem is that shmat() calls do_mmap_pgoff() with MAP_FIXED, and
|
|
the address rounded down to 0. For the regular mmap case, the
|
|
protection mentioned above is that the kernel gets to generate the
|
|
address -- arch_get_unmapped_area() will always check for MAP_FIXED and
|
|
return that address. So by the time we do security_mmap_addr(0) things
|
|
get funky for shmat().
|
|
|
|
The testcase itself shows that while a regular user crashes, root will
|
|
not have a problem attaching a nil-page. There are two possible fixes
|
|
to this. The first, and which this patch does, is to simply allow root
|
|
to crash as well -- this is also regular mmap behavior, ie when hacking
|
|
up the testcase and adding mmap(... |MAP_FIXED). While this approach
|
|
is the safer option, the second alternative is to ignore SHM_RND if the
|
|
rounded address is 0, thus only having MAP_SHARED flags. This makes the
|
|
behavior of shmat() identical to the mmap() case. The downside of this
|
|
is obviously user visible, but does make sense in that it maintains
|
|
semantics after the round-down wrt 0 address and mmap.
|
|
|
|
Passes shm related ltp tests.
|
|
|
|
Link: http://lkml.kernel.org/r/1486050195-18629-1-git-send-email-dave@stgolabs.net
|
|
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
|
|
Reported-by: Gareth Evans <gareth.evans@contextis.co.uk>
|
|
Cc: Manfred Spraul <manfred@colorfullife.com>
|
|
Cc: Michael Kerrisk <mtk.manpages@googlemail.com>
|
|
Cc: <stable@vger.kernel.org>
|
|
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
|
|
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
|
---
|
|
ipc/shm.c | 13 +++++++++----
|
|
1 file changed, 9 insertions(+), 4 deletions(-)
|
|
|
|
diff --git a/ipc/shm.c b/ipc/shm.c
|
|
index d7805ac..06ea9ef 100644
|
|
--- a/ipc/shm.c
|
|
+++ b/ipc/shm.c
|
|
@@ -1091,8 +1091,8 @@ out_unlock1:
|
|
* "raddr" thing points to kernel space, and there has to be a wrapper around
|
|
* this.
|
|
*/
|
|
-long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr,
|
|
- unsigned long shmlba)
|
|
+long do_shmat(int shmid, char __user *shmaddr, int shmflg,
|
|
+ ulong *raddr, unsigned long shmlba)
|
|
{
|
|
struct shmid_kernel *shp;
|
|
unsigned long addr;
|
|
@@ -1113,8 +1113,13 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr,
|
|
goto out;
|
|
else if ((addr = (ulong)shmaddr)) {
|
|
if (addr & (shmlba - 1)) {
|
|
- if (shmflg & SHM_RND)
|
|
- addr &= ~(shmlba - 1); /* round down */
|
|
+ /*
|
|
+ * Round down to the nearest multiple of shmlba.
|
|
+ * For sane do_mmap_pgoff() parameters, avoid
|
|
+ * round downs that trigger nil-page and MAP_FIXED.
|
|
+ */
|
|
+ if ((shmflg & SHM_RND) && addr >= shmlba)
|
|
+ addr &= ~(shmlba - 1);
|
|
else
|
|
#ifndef __ARCH_FORCE_SHMLBA
|
|
if (addr & ~PAGE_MASK)
|
|
--
|
|
cgit v1.1
|
|
|